8yr old battery

I have an 8 yr old battery in a 1994 mercedes c220. It has 42k mileage and 4cylinders. The car continues to start with ease and runs welll. However, I am concerned that I may have trouble starting in this years winter weather. To that end. I have a startup battery booster in my trunk.
I was told that I could damage the alternator if I continued to use this apparently fine functioning old battery. Is this true? Should I change to a new battery despite the old battery's continued utility?
Lwstock